1. Field of the Invention
The present invention relates generally to a process and apparatus for determining damage to cyclically moving machine components such as roller bearings and gears, and a process and apparatus for separating periodic signal portions from a signal, such as a signal for determining damage to cyclically moving machine components.
2. Description of the Prior Art
A survey of devices and apparatus for determining damage on cyclically moving machine components by analysis of a vibration signal recorded by a sensor and caused by the motion can be found in chapter 6.1 of Vibration-diagnostic Assessment of Machines and Systems by Ulrich Klein, where vibration analysis of roller bearings is discussed. The conventional approach consists in coupling a vibration sensor securely to a bearing or to a corresponding machine housing, with a signal which is amplified. The amplified vibration signal is subjected to envelope curve formation by means of bandpass filtering, rectification and subsequent lowpass filtering and the frequency spectrum of the envelope curve signal being formed which is finally analyzed to draw conclusions about damage in the roller bearing. But evaluation methods in the time domain are also known, such as analysis of the envelope curve in the time domain, vibration intensity analysis, and statistical analysis of the time signal.
Examples of evaluation of the envelope curve signal in the time domain can be found in U.S. Pat. Nos. 4,007,630 and 3,554,012, whereby essentially the amplitudes are analyzed. Furthermore, a process is known in which relative extreme values of the bandpass-filtered, rectified and lowpass-filtered vibration signal are determined and stored, the intensity value of each recorded event being multiplied by the previously recorded value and the corresponding product values and the underlying time differences being sent for frequency analysis. The resulting frequency distribution is then subjected to pattern recognition according to stipulated criteria.
Pure frequency analysis processes have the inherent defect that only part of the information contained in the original time signal is contained in the spectrum and can be evaluated. In an analysis of the time signal of cyclically moving machine components, a problem arises in which a host of signals with other periodicities or frequencies. For example, the rotation frequency of the shaft, is superimposed on the signal of interest, for example, excitations which are caused by outer ring damage in a roller bearing and which also occur with the rollover frequency of the outer ring, so that these signals can only be recognized with difficulty even after envelope curve determination in the time domain. Another problem is that the periodicity of the signal portion of interest is very often not exactly known. Thus, in a radial roller bearing the rollover frequency of the outer ring is often a function not only of the rpm of the shaft, but also of the pressure angle, i.e., the axial load on the bearing.
Accordingly, it is an object of the present invention to overcome the disadvantages in the prior art to provide a process and apparatus for determining the damage on cyclically moving machine components which enables analysis of the information contained in the signal caused by the motion of the machine components. Another object of this invention is to devise an effective and flexible process and apparatus for separating the periodic signal portions from a signal.
The first object of the present invention is achieved by separating one signal portion with an adjustable period to make possible more accurate and more complete analysis of the signal since different machine components differ by different characteristic period durations in which significant damage signals can be expected. Thus, in a roller bearing the signal portions caused by outer ring damage, rolling element damage and inner ring damage generally occur with different period lengths. Separation of these signal portions in accordance with the invention allows more detailed damage analysis.
It is advantageous in achieving the second object of the invention by synchronizing the rotation frequency of the ring storage to the period length of the desired signal portions, to enable simple, flexible and reliable separation of the periodic signal portions from one signal. Each storage element preferably act as a lowpass filter for the input signal, and this action can be digitally simulated. Preferably, the ring storage is made digitally, the storage elements being formed as cyclically addressed accumulators. Frequency matching of the ring storage rotation can on the one hand be done by the period duration of the desired signal portions being determined from the signal, for example, by means of search tone analysis, Fourier transform or cepstrum analysis and the storage being rotated with the frequency determined in this way. Alternatively, rotation of the ring storage can be directly synchronized with the input signal, and this can occur by means of a phase shifter, whereby the contents of the storage elements being multiplied by the derivative of the input signal and the result being accumulated and at certain instants the rotation frequency of the ring storage being changed according to the accumulated value. Moreover, preferably the shape of the input signal for synchronization is processed, and it can be lowpass filtration or the portions which do not have the period duration of the desired signal are removed from the input signal by means of another rotating ring storage.
Preferably, the aspects of the present invention are used for the vibrational analysis of machine components such as roller bearings, gears or rollers for the continuous manufacture of a product, whereby the components stamp the surface of the product. In the case of a roller bearing, preferably one period form filter each is assigned to the outer ring, the inner ring and/or the rolling elements, and each have rotation frequencies which correspond to the outer ring rollover frequency, the inner ring rollover frequency and the rolling element rollover frequency. In addition, preferably the output signal of the other period form filter at the time is subtracted from the signal before it is supplied to the respective period form filter as the input signal to remove signal portions which have the xe2x80x9cwrongxe2x80x9d periodicity. There is preferably another period form filter which is synchronized to the rpm of the shaft and which has an output signal which is subtracted from the signal before it is supplied to other period form filters as the input signal. Furthermore, the change of the contents of the ring storage of the period form filter in time can be analyzed for the outer ring, the inner ring and the rolling elements in order to determine the unbalance or balanced load acting on the bearing. The sum of the balanced load and the unbalance can be determined by forming the ratio between the amplitudes of the signal portions originating from the inner ring contact and the outer ring contact for the output signal of the roller bearing period form filter.
Furthermore, period form filters can also be used to determine from the rotation frequency of the ring storage the rollover frequencies of the outer ring, the inner ring and the rolling element and from them the pressure angle and the contact angle of the roller bearing. Instead of a common period form filter for all rolling elements, one period form filter can also be assigned to the each rolling element individually. To counteract possible slip of the rolling element outside the load region, the quality of the rolling element period form filter can be set such that it oscillates transiently within one cage revolution. In doing so, for each cage revolution its own map of the contents of the ring storage can be produced, the phase shift of different maps being determined and the maps being corrected with respect to this phase shift and then added to form the output signal. Alternatively, the phase of rotation of the ring storage of the rolling element period form filter can be controlled according to the ascertained slip angle to compensate for rolling element slip. In this case, the phase-staggered addition of the individual images is not necessary. If neither phase correction of the signals or the maps nor phase correction of the rotation of the ring storage is undertaken, then the unknown rolling element slip can be compensated by sorting the output signal of the period form filter for the rolling elements by its amplitude, from which then the damage length for the rolling elements can be determined.